<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .search {
            position: relative;
            width: 150px;
            margin: 100px auto;
        }

        .box1 {
            position: absolute;
            top: -40px;
            width: 150px;
            height: 30px;
            box-shadow: 4px 5px 10px rgba(0, 0, 0, 0.425);
        }

        .box1::before {
            content: '';
            position: absolute;
            top: 27px;
            left: 19px;
            width: 0;
            height: 0;
            border: solid 8px transparent;
            border-top-color: #fff;
        }

        .search input {
            width: 150px;
        }
    </style>
</head>

<body>
    <div class="search">
        <div class="box1"></div>
        <input type="text" placeholder="请输入单号">
    </div>
</body>

</html>